This invention relates to the use and operation of electromechanical valve actuators. More particularly, it relates to a new device that enables the operator of a valve actuator to have a visual indication of whether the actuator is open, closed or in a mid-travel position.
In many fields, valve actuators are used to open and close valves that control fluid flow. Reference is made to our copending U.S. Pat. application, Ser. No. 188,357, incorporated herein by reference. These electromechanical valve actuators can be found at power generating stations, chemical manufacturing plants, and oil refineries, to name just a few, and they control the opening and closing of the valve and limit the torque and thrust applied to the valve stem. In most all of these situations, the operator must be able to accurately know from his central location what position the valve stem is in and efficiently and quickly control its operation.
Most electromechanical valve actuators contain a geared limit switch which is gear-driven from the actuator power train. The geared section of the switch is essentially a mechanical counter used to count actuator drive sleeve turns. Drive sleeve turns (clockwise or counter-clockwise) are used to predict valve stem location, such as open, closed or mid-travel. The counter section of the geared limit switch may be disengaged (via a clutch) so that counter travel may be set to agree with distinct valve stem locations, i.e. open, closed or mid-travel. When the counter travels through the set points of the switch, the rotary output, taken off of the rotor of the geared counter, is used to make or break electrical contacts.
When it was necessary to have a visual indication of valve position, a practice has been to use the geared limit switch drive as an input to such visual indication. The geared limit switch, which has a plurality of rotors connected to it, is directly connected to the valve drive sleeve which is connected to the valve stem nut, which is connected to the valve stem, which is connected to the valve. Once valve location was analyzed and the number of valve stem turns reconciled with valve position, a device known as a "continuous indicator", was attached to the rotors and used as a position indicator. When using this device, each valve actuator had to be individually analyzed and a special gear box constructed and connected to the rotors so that stem rotations would be indicated on a dial or other visual indicator. This apparatus and the procedure have the disadvantages of requiring a customized gear drive for each valve and the associated labor costs necessary to properly complete the installation work.